"All students are safe in their classrooms and will remain there until the police give the all clear."
Exams were also cancelled this afternoon, the school's statement said.
"Any students with exams this afternoon need to stay away from the school.
"Parents are requested not to enter the school grounds until the police lift the lockdown.
"We will keep everyone informed with any changes as soon as we can."
A Cambridge resident said her son's friend had gone to the school for an exam and texted her about the lockdown.
"After her exam finished this morning, straightway they were put into lockdown and told to find the closest classroom.
"The kids haven't been told anything so have no idea what's going on."
The school had been in lockdown since 10.50am, she said.
A police spokesperson earlier said officers were in attendance on Swayne Rd in Cambridge where a report was received around 10.40am of a male in possession of a weapon.
"Police have asked Cambridge High School and other nearby schools and early childhood centres to keep their students inside while officers attend and work to locate the male."